I recall reading many years ago that the reason the National Airport metro station was built above ground was because it was hoped that it would be more visible and draw more passengers from Crystal City that way. It never did, especially after the parking structures were constructed. Instead, recently arrived air passengers have ever since had to stand on an outdoor station platform that can get brutally cold in winter with the wind blowing in from the Potomac, and stiflingly hot in the summer.

If I'm remembering that motivation correctly, evidently Arlington is still trying to make it happen.